The present invention relates to a method for surface coloring plastic objects after manufacture.
It is known that the market increasingly demands the thermal dye-sublimation printing method to produce particular aesthetic effects on a wide range of products or for reproducing images on objects of various kinds.
This context accordingly includes the manufacture of products having a simple structure and considerable dimensions, such as plastic surfaces of pieces of furniture printed so as to imitate wood or marble, but also of small objects having a complex structure, such as containers for cosmetics, ornamental objects, small electric household appliances and frames for glasses, in which various and mostly complex color effects are obtained.
These productions are currently performed by means of thermal sublimation dyes which are deposited on a sheet substrate arranged so as to cover the parts to be treated and are then heated, together with the object being treated, to a temperature whereat the dyes sublimate and fix to the object.
One of the current problems of this type of treatment is due to the fact that the sublimation temperature is around 150-200.degree. C., which is unacceptably high for many of the plastics employed, such as ABS, acetal plastics, styrenes and acetates,-whose structure softens when heated to the temperature whereat the pigments sublimate.
This is a considerable limitation, because softening in practice leads, on subsequent cooling, to deformations of the product compromising its quality and the possibility to market it.
As an alternative to the transfer of dyes by sublimation, screen-printing or tampographic methods are used; however, they are adapted for objects having a simple and not particularly complex shape.